In elevator systems the mass of the load moved with the motor is to a great extent dependent on the lifting height of the elevator. In elevators of high lifting heights the hoisting ropes are long and the motor must be able to move also the roping, in addition to the elevator car and the load. Long and thick ropes are heavy and set challenging power requirements for the hoisting machinery especially in acceleration situations, when the power required from the hoisting machinery is at its greatest.
Elevators of a high lifting height that move the elevator car via ropes by means of a traction sheave rotated by an electric motor are prior art. It is prior art to dimension such a large motor in terms of its output power capacity for the hoisting machinery of an elevator of a high lifting height that it performs its task alone. As the heights of buildings, and thus also lifting heights, grow it would thus become necessary to arrange increasingly larger motors in new buildings. A motor of the desired size range is not always necessarily available, however. Additionally, taking a heavy motor of large size into the machine room may be awkward owing to the cramped spaces. That being the case, in elevator systems possessing a high lifting height, in other words in high-rise elevators, using only one motor is not always advantageous. The object of the invention is suited for use in super-high-rise elevators with machine room, which have a very high lifting height even on the high-rise scale. The machinery size of these kinds of elevators may exceed, in terms of their width, even the size of the cross-section of the elevator shaft, if the machinery comprises only one extremely large motor. The machine room should thus be very wide, possibly disadvantageously wide, compared to the space taken by the elevator on the other floors of the building, in which case e.g. problems can be caused in the design of the bearing structures of the building by, among other reasons, causing a discontinuity in the structures at the point of the machine room. Another drawback in using one enormous machine size is that, owing to their rarity, production quantities are so small that their manufacturing costs would be exceptionally large.
Elevators, especially elevators without machine room, the ropes of which are moved with two traction shaves, which traction sheaves are rotated by separate electric motors, are also prior art. It is prior art to install these motors and traction sheaves in the same elevator shaft. In this case the hoisting load can be divided between two traction sheaves and the motor rotating them. One advantage, among others, is that despite the increase in machinery size, a spacious elevator car fits into the shaft and the cross-section of the elevator shaft can be utilized effectively throughout the entire length of the shaft.